Null references (oh no, not again!)

[Daniel Keep]

Just noticed this hit Slashdot, and thought I might repost the abstract
here.

http://qconlondon.com/london-2009/presentation/Null+References:+The+Billion+Dollar+Mistake

> I call it my billion-dollar mistake. It was the invention of the null
> reference in 1965. [...] This has led to innumerable errors,
> vulnerabilities, and system crashes, which have probably caused a
> billion dollars of pain and damage in the last forty years. [...] More
> recent programming languages like Spec# have introduced declarations
> for non-null references. This is the solution, which I rejected in
> 1965.

  -- Sir Charles Hoare, Inventor of QuickSort, Turing Award Winner

Serendipitous, since I just spent today trying to track down an
(expletives deleted) obscure null dereference problem.  I figure I must
be in good company if even the guy who invented null doesn't like it...

It also make me look up this old thing; it's several years old now, but
I still think it's got some good points in it.

http://www.st.cs.uni-saarland.de/edu/seminare/2005/advanced-fp/docs/sweeny.pdf

> * Accessing arrays out-of-bounds
> * Dereferencing null pointers
> * Integer overflow
> * Accessing uninitialized variables
>
> 50% of the bugs in Unreal can be traced to these problems!

Tim Sweeny isn't an amateur; he's responsible, at least in part, for one
of the most commercially successful game engines ever.  I figure if even
he has trouble with these things, it's worth trying to fix them.

Note that D already solves #1 and #4, LDC could give us #3... that just
leaves #2.  :D

  -- Daniel